Some vehicles use dynamic or regenerative braking to slow or stop movement of the vehicles. This type of braking can involve obtaining energy from traction motors of the vehicles (when the motors are rotated by the movement of the vehicles instead of the motors rotating to move the vehicles) and dissipating this energy in resistance grids.
During high speed travel, however, the available braking effort or braking horse power that is available from dynamic braking may be limited by the stability of the traction motors at the high speeds. The braking capability may be limited by a motor breakdown margin available at the link voltage of operation.
To maintain sufficient braking capability, one or more of the resistance grids may need to be disconnected from a circuit that connects the grids with the traction motors to allow sufficient braking resistance for maintaining stable operation of the vehicle. Disconnecting a parallel resistance grid, however, can lead to a significant loss of braking horse power and may not be desired by many vehicle operators.